Power Management Low-Cost, Two-Cell Li-Ion/Li-Pol Battery Charger with Cell-Balancing Support Specification Sheet
AN2309
November 25, 2007 Document No. 001-17394 Rev. *B - 17 -
Cell-Balancing Parameters
All cell-balancing parameters are located in the header file globdefs.h in the project folder. The header file globdefs.h contains
the following parameters:
Table 3. Cell-Balancing Parameters
Parameter
Unit
Description
Vmeas_err
V
Resistor Matrix Error for Measuring Cell Voltage
Vin_err
V
Internal Cell Impedance Error
Vch_bal_min
V
Minimum Cell Balance for Charge Phase
Vdisch_bal_min
V
Minimum Cell Balance for Discharge Phase
Vdisch_mid
V
Voltage of 50 Percent Charging Cell During Discharge Phase
Ibal_min
A
Minimum Charge Current Value When the Cell Balancing is Allowed (on
CV Phase)
T_BAL_INTERVAL
second
Cell-Balancing Interval
Conclusion
A two-cell battery charger with cell-balancing technology has
been described. Recommendations for cell-balancing circuit
components are given. An effective cell-balancing algorithm
for both charge and discharge phases is developed. The
algorithm avoids problems that can arise in a battery pack
with two cells in series. By altering several configuration
parameters, the cell-balancing algorithm can easily be
adapted for various applications and selected batteries. A
method to perform cell balancing is proposed that uses
charge/discharge phases that do not significantly lengthen
charge times. This two-cell battery charger supports the
pulse charge technique.
The two-cell battery charger algorithm and cell-balancing
algorithm are implemented in the PSoC device firmware.
The dedicated PC-based software is developed to perform
real-time charging and cell-balancing process visualization
and analysis through a graphical user interface. The
proposed device can be used as a complete battery pack
management system for laptop computers, and medical,
industrial, and other applications. References have been
made to AN2294 if users are interested in easily adding fuel
gauge functionality to this project. The unique architecture of
the PSoC device and the in-circuit and self-programming
capabilities make these operations simple. The chosen
CY8C24x23A PSoC device family further reduces total
system cost.
Figure 12. Two-Cell Battery Charger Photograph, Actual Size
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